Scientists have used the world's largest robotic telescope to make the earliest-ever
measurement of the optical polarisation of a Gamma Ray Burst (GRB) just 203
seconds after the start of the cosmic explosion. This finding, which provides
new insight into GRB physics, is published in Science today (15th
March 2007).

The scientists from Liverpool John Moores University and colleagues in the UK, Italy,
France and Slovenia used the Liverpool Telescope on the island of La Palma and
its novel new polarimeter, RINGO, to perform the measurement following
detection of the burst by NASA's Swift satellite.

Gamma Ray Bursts are the most instantaneously powerful explosions in the Universe and are
identified as brief, intense and completely unpredictable flashes of high
energy gamma rays on the sky. They are thought to be produced by the death
throes of a massive star and signal the birth of a new black hole or neutron
star (magnetar) and ejection of an ultra-high speed jet of plasma. Until now,
the composition of the ejected material has remained a mystery and, in
particular the importance of magnetic fields has been hotly debated by GRB
scientists.

The Liverpool
measurement was obtained nearly 100 times faster than any previously published
optical polarisation measurement for a GRB afterglow and answers some
fundamental questions about the presence of magnetic fields.

Principal
author of the Science paper and GRB team leader Dr Carole Mundell of the
Astrophysics Research Institute, Liverpool John Moores University, said
"Our new measurements, made shortly after the Gamma Ray Burst, show that
the level of polarisation in the afterglow is very low. Combined with our knowledge of how the
light from this explosion faded, this rules-out the presence of strong magnetic
fields in the emitting material flowing out from the explosion - a key element
of some theories of GRBs."

The
so-called optical afterglow is thought to originate from light emitted when
this ejected material impacts the gas surrounding the star. In the first few
minutes after the initial burst of gamma rays, the optical light carries
important clues to the origin of these catastrophic explosions; capturing this
light at the earliest possible opportunity and measuring its properties is
ideally suited to the capabilities of large robotic telescopes like the
Liverpool Telescope.

Lord Martin Rees, Astronomer Royal
and President of the Royal Society said "We are still flummoxed about the
underlying 'trigger' for gamma ray bursts, and why they sometimes emit bright
flashes of light. Theorists have a lot of tentative ideas, and these
observations narrow down the range of options."

Professor Keith Mason, CEO of the Particle Physics and Astronomy Council
(PPARC) and UK lead investigator on Swift's Ultra Violet/Optical Telescope,
said, "This result demonstrates well the effectiveness of Swift's rapid response
alert system, allowing robotic telescopes, such as the Liverpool Telescope,
to follow up gamma ray bursts within seconds, furthering our knowledge with
each detection."